RFID tags can be used to control the movement of people within a designated perimeter. Examples of such use include infant or pediatrics patient protection in a care facility, elder-care wander prevention, or house arrest enforcement where a tagged person is restricted to a monitored area. Effective perimeter restriction is only possible if an alarm is generated when the tag is removed from a monitored person's body.
Existing RFID tag-bands employ a variety of methods to maintain continuity, including embedding conductive traces within or through the band, using a band made entirely of electrically conductive material, optical signal transmission through the optically conductive band, optically conductive fiber(s) embedded within the band, and electromagnetic or capacitive coupling between the band and the tag.
Presently, detection of RFID tag band removal is done by monitoring conductivity of the following electrical current path: A current source within the RFID tag initiates electrical current flow from a metal contact to the outside of the RFID tag enclosure; A mechanical bond is made between metallic contact and an electrically conductive band made out of flexible material with embedded metal conductors; The mechanical bond is semi-secure with intention to reliably maintain electrical contact during normal use; On the other side of the band, there is another metal contact on tag's enclosure which enables electrical current to enter the enclosure and be detected by electronic circuitry.
Any break in electrically conductive path is considered a breach in tag attachment and Tamper Alarm is declared. This conductive path break can come from the band being cut or from detachment between the band and the metal contacts on the tag enclosure. Band cut is always a legitimate cause for signalling tamper alarm, but interruption in electrical current flow between the tag enclosure contacts and the band can occur not only due to physical detachment between the contact and the band, but also due to decreased conductivity which can, and frequently does, occur due to oxidation of metallic contacts or unreliable bond between the contacts and the metallic conductors within the band. The oxidation occurs as a result of cleaning the tag body after every use, usually with aggressive solutions. This is the cause of many false Tamper Alarms.
Some cut-band RFID tags are based on the principle of detecting conductivity of the band surface or conductivity of the band itself (when the entire band is made out of electrically conductive material). In this case, there is a potential for defeating the capability of the tag to detect when the band is being cut by a jumper wire with 2 alligator clips on each end of the wire and clamping alligator clips to the band in a way that they make conductive contact with exposed and conductive parts of the band. In such a case “alligator clip wire” creates a shunt for electrical current and if the band is cut between two alligator clips, the tag can be removed from the person, without detection that the band is cut because the current continues to flow through the alligator clip wire. This is a potential security breach which can be very easily exploited on some bands, that is desirable to eliminate.
Present cut-band RFID tag devices using embedded conductive materials (fibers, traces) are often prone to false alarms due to open circuits caused by normal user wear. What is needed is a cut-band tamper-signalling RFID tag which allows for robust movement of the band and band to tag connection without triggering false alarms, while maintaining the electrical integrity of the device from tampering and attempts to circumvent or remove. Additionally, there are maintenance issues with pre-existing RFID conductive band tags. It would be useful to be able to re-use expensive RFID elements while readily disposing, for hygenic reasons, of conductive band portions that have been used for a designated duration of time on a patient.